Millstone Kernkraftwerk

Report by Laura Harris

Fall 1995

This past summer I worked at the millstone nuclear power plant and learned a great deal about nuclear energy.

A nuclear power plant uses nuclear fission to produce electricity. The fuel used is uranium-235, an unstable element. When a neutron encounters a uranium nucleus, the nucleus is split and energy is released. This begins a chain reaction, in which each nucleus releases one neutron. These neutrons can split several uranium nuclei.

Each nuclear power plant has a reactor building, which is encased in think concrete. Inside is the reactor with its nuclear fuel and the control rods. The control rods are used to absorb the neutrons in order to control the reaction. The reactor also contains water to slow the neutrons and to cool down the chain reaction. Most of the nuclear power plants in the United States are light-water reactors, which use light water as the cooling water for the reactor.

There are two types of nuclear power plant, the pressurized water reactor and the boiling-water reactor. In the pressurized-water reactor, steam is produced outside of the reactor. The pumps produce an extremely high pressure in the primary loop, to prevent the heated water from boiling. This hot water passes then through a heat exchanger where water is heated that is boiled in the secondary loop. The steam produced is used to power a turbine. When the steam turbine is working the generator can then produce electricity. Afterwards the steam passes through a condenser where ocean water is used to condense the steam. The condensed water can be used again and goes through the steam generator once more. The difference between a pressurized water reactor and a boiling water reactor is that the latter produces steam inside the reactor. The pressure of the reactor cooling water is not very high and it therefore boils. This steam is used directly in the boiling-water reactor to turn the steam turbine. Afterwards the condenser condenses the steam, which is then used as again.

I believe that the pressurized water reactor is slightly preferable, because the primary circulation is separate. The primary circulation loop is contaminated, and therefore it is better if it is contained within the reactor building. The secondary loop is separate, which means that the water used, the condensed water, the steam produced, and the steam turbine remain clean. But in the boiling water reactor the contaminated water is not separate. Therefore, the boiling water, the condenser cooling water, the steam produced, and the steam turbine are also contaminated. Due to the threat that radiation poses to health, I believe it is better to keep this water contained within the reactor.